Classifications

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  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G18/00—Polymeric products of isocyanates or isothiocyanates
  • C08G18/06—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen
  • C08G18/28—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen characterised by the compounds used containing active hydrogen
  • C08G18/2805—Compounds having only one group containing active hydrogen
  • C08G18/285—Nitrogen containing compounds
  • C08G18/2875—Monohydroxy compounds containing tertiary amino groups
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
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  • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
  • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
  • H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer
  • H01L21/50—Assembly of semiconductor devices using processes or apparatus not provided for in a single one of the subgroups H01L21/06 - H01L21/326, e.g. sealing of a cap to a base of a container
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  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F283/00—Macromolecular compounds obtained by polymerising monomers on to polymers provided for in subclass C08G
  • C08F283/006—Macromolecular compounds obtained by polymerising monomers on to polymers provided for in subclass C08G on to polymers provided for in C08G18/00
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
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  • C08F283/00—Macromolecular compounds obtained by polymerising monomers on to polymers provided for in subclass C08G
  • C08F283/12—Macromolecular compounds obtained by polymerising monomers on to polymers provided for in subclass C08G on to polysiloxanes
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  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F290/00—Macromolecular compounds obtained by polymerising monomers on to polymers modified by introduction of aliphatic unsaturated end or side groups
  • C08F290/08—Macromolecular compounds obtained by polymerising monomers on to polymers modified by introduction of aliphatic unsaturated end or side groups on to polymers modified by introduction of unsaturated side groups
  • C08F290/14—Polymers provided for in subclass C08G
  • C08F290/147—Polyurethanes; Polyureas
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F290/00—Macromolecular compounds obtained by polymerising monomers on to polymers modified by introduction of aliphatic unsaturated end or side groups
  • C08F290/08—Macromolecular compounds obtained by polymerising monomers on to polymers modified by introduction of aliphatic unsaturated end or side groups on to polymers modified by introduction of unsaturated side groups
  • C08F290/14—Polymers provided for in subclass C08G
  • C08F290/148—Polysiloxanes
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F299/00—Macromolecular compounds obtained by interreacting polymers involving only carbon-to-carbon unsaturated bond reactions, in the absence of non-macromolecular monomers
  • C08F299/02—Macromolecular compounds obtained by interreacting polymers involving only carbon-to-carbon unsaturated bond reactions, in the absence of non-macromolecular monomers from unsaturated polycondensates
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
  • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
  • H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer
  • H01L21/50—Assembly of semiconductor devices using processes or apparatus not provided for in a single one of the subgroups H01L21/06 - H01L21/326, e.g. sealing of a cap to a base of a container
  • H01L21/56—Encapsulations, e.g. encapsulation layers, coatings
  • H01L21/563—Encapsulation of active face of flip-chip device, e.g. underfilling or underencapsulation of flip-chip, encapsulation preform on chip or mounting substrate
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L23/00—Details of semiconductor or other solid state devices
  • H01L23/28—Encapsulations, e.g. encapsulating layers, coatings, e.g. for protection
  • H01L23/29—Encapsulations, e.g. encapsulating layers, coatings, e.g. for protection characterised by the material, e.g. carbon
  • H01L23/293—Organic, e.g. plastic
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L24/00—Arrangements for connecting or disconnecting semiconductor or solid-state bodies; Methods or apparatus related thereto
  • H01L24/01—Means for bonding being attached to, or being formed on, the surface to be connected, e.g. chip-to-package, die-attach, "first-level" interconnects; Manufacturing methods related thereto
  • H01L24/26—Layer connectors, e.g. plate connectors, solder or adhesive layers; Manufacturing methods related thereto
  • H01L24/28—Structure, shape, material or disposition of the layer connectors prior to the connecting process
  • H01L24/29—Structure, shape, material or disposition of the layer connectors prior to the connecting process of an individual layer connector
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L24/00—Arrangements for connecting or disconnecting semiconductor or solid-state bodies; Methods or apparatus related thereto
  • H01L24/98—Methods for disconnecting semiconductor or solid-state bodies
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L2224/00—Indexing scheme for arrangements for connecting or disconnecting semiconductor or solid-state bodies and methods related thereto as covered by H01L24/00
  • H01L2224/73—Means for bonding being of different types provided for in two or more of groups H01L2224/10, H01L2224/18, H01L2224/26, H01L2224/34, H01L2224/42, H01L2224/50, H01L2224/63, H01L2224/71
  • H01L2224/732—Location after the connecting process
  • H01L2224/73201—Location after the connecting process on the same surface
  • H01L2224/73203—Bump and layer connectors
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
  • H01L2924/01—Chemical elements
  • H01L2924/01012—Magnesium [Mg]
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
  • H01L2924/01—Chemical elements
  • H01L2924/01019—Potassium [K]
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
  • H01L2924/01—Chemical elements
  • H01L2924/01046—Palladium [Pd]
• • H—ELECTRICITY
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  • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
  • H01L2924/01—Chemical elements
  • H01L2924/01077—Iridium [Ir]
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
  • H01L2924/01—Chemical elements
  • H01L2924/01087—Francium [Fr]
• • H—ELECTRICITY
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  • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
  • H01L2924/10—Details of semiconductor or other solid state devices to be connected
  • H01L2924/102—Material of the semiconductor or solid state bodies
  • H01L2924/1025—Semiconducting materials
  • H01L2924/10251—Elemental semiconductors, i.e. Group IV
  • H01L2924/10253—Silicon [Si]
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  • H01L2924/10—Details of semiconductor or other solid state devices to be connected
  • H01L2924/11—Device type
  • H01L2924/14—Integrated circuits
• • H—ELECTRICITY
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  • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
  • H01L2924/15—Details of package parts other than the semiconductor or other solid state devices to be connected
  • H01L2924/181—Encapsulation
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S428/00—Stock material or miscellaneous articles
  • Y10S428/901—Printed circuit
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T29/00—Metal working
  • Y10T29/49—Method of mechanical manufacture
  • Y10T29/49002—Electrical device making
  • Y10T29/49117—Conductor or circuit manufacturing
  • Y10T29/49124—On flat or curved insulated base, e.g., printed circuit, etc.
  • Y10T29/4913—Assembling to base an electrical component, e.g., capacitor, etc.
  • Y10T29/49146—Assembling to base an electrical component, e.g., capacitor, etc. with encapsulating, e.g., potting, etc.
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/31504—Composite [nonstructural laminate]
  • Y10T428/31678—Of metal
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/31504—Composite [nonstructural laminate]
  • Y10T428/31678—Of metal
  • Y10T428/31692—Next to addition polymer from unsaturated monomers

Definitions

• This invention relates to a method of making an electronic component using a reworkable underfill encapsulant composition.
• Underfill encapsulant compositions protect and reinforce the interconnections between an electronic component and a substrate.
• Microelectronic devices contain millions of electrical circuit components, mainly transistors assembled in integrated circuit (IC) chips, but also resistors, capacitors, and other components. These electronic components are interconnected to form the circuits, and eventually are connected to and supported on a carrier or substrate, such as a printed wire board.
• IC integrated circuit
• the integrated circuit component may comprise a single bare chip, a single encapsulated chip, or an encapsulated package of multiple chips.
• the single bare chip can be attached to a lead frame, which in turn is encapsulated and attached to the printed wire board, or it can be directly attached to the printed wire board.
• the connections are made between electrical terminations on the electronic component and corresponding electrical terminations on the substrate.
• One method for making these connections uses metallic or polymeric material that is applied in bumps to the component or substrate terminals. The terminals are aligned and contacted together and the resulting assembly heated to reflow the metallic or polymeric material and solidify the connection.
• the electronic assembly is subjected to cycles of elevated and lowered temperatures. Due to the differences in the coefficient of thermal expansion for the electronic component, the interconnect material, and the substrate, this thermal cycling can stress the components of the assembly and cause it to fail. To prevent failure, the gap between the component and the substrate is filled with a polymeric encapsulant, hereinafter called underfill or underfill encapsulant, to reinforce the interconnect and to absorb some of the stress of the thermal cycling.
• underfill or underfill encapsulant a polymeric encapsulant
• the underfill encapsulation may take place after the reflow of the metallic or polymeric interconnect, or it may take place simultaneously with the reflow. If underfill encapsulation takes place after reflow of the interconnect, a measured amount of underfill encapsulant material will be dispensed along one or more peripheral sides of the electronic assembly and capillary action within the component-to-substrate gap draws the material inward.
• the substrate may be preheated if needed to achieve the desired level of encapsulant viscosity for the optimum capillary action. After the gap is filled, additional underfill encapsulant may be dispensed along the complete assembly periphery to help reduce stress concentrations and prolong the fatigue life of the assembled structure. The underfill encapsulant is subsequently cured to reach its optimized final properties.
• the underfill encapsulant which can include a fluxing agent if solder is the interconnect material, first is applied to either the substrate or the component; then terminals on the component and substrate are aligned and contacted and the assembly heated to reflow the metallic or polymeric interconnect material. During this heating process, curing of the underfill encapsulant occurs simultaneously with reflow of the metallic or polymeric interconnect material.
• thermosetting organic materials the most widely used being epoxy/anhydride systems.
• relatively high molecular weight thermoplastics would be the preferred compositions for underfill materials.
• These materials however, have high viscosity or even solid film form, which are drawbacks to the manufacturing process.
• This invention is a method for making an electronic assembly consisting of an electronic component, such as a flip-chip or a ball grid array, connected to a substrate and reinforced with a reworkable underfill encapsulant composition.
• the underfill encapsulant composition comprises one or more compounds containing one or more maleimide functionality, or one or more compounds containing one or more vinyl functionality, or a combination of compounds containing maleimide or vinyl functionality, a free-radical initiator and/or a photoinitiator, and optionally one or more fillers.
• a compound containing one maleimide functionality will be referred to hereinafter as a mono-functional maleimide compound.
• a compound containing more than one maleimide functionality will be referred to hereinafter as a poly-functional maleimide compound.
• a compound containing one vinyl functionality will be referred to hereinafter as a mono-functional vinyl compound.
• a compound containing more than one vinyl functionality will be referred to hereinafter as a poly-functional vinyl compound.
• the functionality is defined herein to be a carbon to carbon double bond.
• the composition is designed to be reworkable by choosing a major amount of mono-functional compounds for the composition.
• the ability to process these thermoplastic compositions for underfill encapsulants is achieved by using relatively low molecular weight reactive oligomers or pre-polymers and curing them in situ after application to the electronic assembly.
• the relatively low molecular weight translates to a lower viscosity and ease of application to the substrate.
• the electronic component has a plurality of electrical terminations, each termination electrically and mechanically connected by a metallic or polymeric material (the metallic or polymeric material also referred to herein as interconnect or interconnect material) to a substrate having a plurality of electrical terminations corresponding to the terminations of the electronic component.
• the underfill encapsulant composition is disposed between the electronic component and the substrate to reinforce the metallic or polymeric interconnect.
• the method of making the electronic assembly comprises the steps:
• the maleimide and vinyl compounds used in the underfill encapsulant compositions of this invention are curable compounds, meaning that they are capable of polymerization, with or without crosslinking.
• to cure will mean to polymerize, with or without crosslinking.
• Cross-linking as is understood in the art, is the attachment of two polymer chains by bridges of an element, a molecular group, or a compound, and in general will take place upon heating. As cross-linking density is increased, the properties of a material can be changed from thermoplastic to thermosetting.
• the underfill encapsulants of this invention will be prepared from mono-functional compounds to limit the cross-link density.
• a minor amount of poly-functional compounds can be added to provide some cross-linking and strength to the composition, provided the amount of poly-functional compounds is limited to an amount that does not diminish the desired thermoplastic properties.
• the cross-link density can also be controlled to give a wide range of glass transition temperatures in the cured underfill to withstand subsequent processing and operation temperatures.
• the Tg is chosen to be below the reflow temperature of the metallic or polymeric interconnect. If the underfill is added after the reflow of the interconnect material, the low Tg will allow the encapsulant material to soften and adhere to both the electronic component and the substrate without affecting the interconnect.
• underfill is added before the reflow, the same effect is achieved.
• the underfill encapsulant will soften and adhere to the electronic component and substrate during the reflow of the interconnect material. Intimate contact is maintained with the interconnect after the interconnect solidifies, imparting good stress transfer and long-term reliability.
• the electronic component can be pried off the substrate, and any residue underfill can be heated until it softens and is easily removed.
• the maleimide compounds and the vinyl compounds may be used independently, or in combination.
• the maleimide or vinyl compounds, or both, will be present in the curable underfill encapsulant compositions in an amount from 2 to 98 weight percent based on the organic components present (excluding any fillers).
• the underfill encapsulant compositions will further comprise at least one free-radical initiator, which is defined to be a chemical species that decomposes to a molecular fragment having one or more unpaired electrons, highly reactive and usually short-lived, which is capable of initiating a chemical reaction by means of a chain mechanism.
• the free-radical initiator will be present in an amount of 0.1 to 10 percent, preferably 0.1 to 3.0 percent, by weight of the maleimide or vinyl compound, or a combination of both maleimide and vinyl compounds (excluding any filler).
• the free radical curing mechanism gives a fast cure and provides the composition with a long shelf life before cure.
• Preferred free-radical initiators include peroxides, such as butyl peroctoates and dicumyl peroxide, and azo compounds, such as 2,2'-azobis(2-methyl-propanenitrile) and 2,2'-azobis(2-methyl-butanenitrile).
• the underfill encapsulant compositions may contain a photoinitiator in lieu of the free-radical initiator, and the curing process may then be initiated by UV radiation.
• the photoinitiator will be present in an amount of 0.1 to 10 percent, preferably 0.1 to 3.0 percent, by weight of the maleimide or vinyl compound, or a combination of both maleimide and vinyl compounds (excluding any filler).
• both photoinitiation and free-radical initiation may be desirable.
• the curing process can be started by UV irradiation, and in a later processing step, curing can be completed by the application of heat to accomplish a free-radical cure.
• these compositions will cure within a temperature range of 80° to 180°C, and curing will be effected within a length of time of 5 minutes to 4 hours.
• the time and temperature curing profile for each encapsulant composition will vary, and different compositions can be designed to provide the curing profile that will be suited to the particular industrial manufacturing process.
• inert inorganic fillers are used in the underfill encapsulant to adjust the coefficient of thermal expansion to more closely mirror that of the circuit interconnect, and to mechanically reinforce the interconnect.
• suitable thermally conductive fillers include silica, graphite, aluminum nitride, silicon carbide, boron nitride, diamond dust, and clays. The fillers will be present typically in an amount of 20 to 80 percent by weight of the total underfill encapsulant composition.
• C(O) refers to a carbonyl group
• the maleimide compounds suitable for use in the circuit component compositions of this invention have a structure represented by the formula: [M ⁇ X m ] n ⁇ Q, or by the formula: [M ⁇ Z m ] n ⁇ K.
• the compound when lower case “n” is the integer 1, the compound will be a mono-functional compound; and when lower case “n” is an integer 2 to 6, the compound will be a poly-functional compound.
• X is structure (II), (III), (IV) or (V), and more preferably is structure (II).
• Q is a linear or branched chain alkyl, alkyloxy, alkylene, or alkyleneoxy species having up to about 100 atoms in the chain, as described with pendant saturated or unsaturated cyclic or heterocyclic substituents, or a siloxane as described, and more preferably is a linear or branched chain alkyl species or siloxane, as described.
• Z is a linear or branched chain alkyl, alkyloxy, alkylene, or alkyleneoxy species having up to about 100 atoms in the chain, as described with pendant saturated or unsaturated cyclic or heterocyclic substituents, or a siloxane as described, and more preferably is a linear or branched chain alkyl species or siloxane, as described.
• K is structure (VIII), (X) or (XI), more preferably is structure (X) or (XI), and most preferably is structure (X).
• the more preferred maleimide compounds are N-butylphenyl maleimide and N-ethylphenyl maleimide.
• R 1 and R 2 are H or an alkyl having 1 to 5 carbon atoms, or together form a 5 to 9 membered ring with the carbons forming the vinyl group;
• B is C, S, N, O, C(O), O-C(O), C(O)-O, C(O)NH or C(O)N(R 8 ), in which R 8 is C 1 to C 5 alkyl;
• m is 0 or 1;
• n is 1-6; and
• X, Q, Z, and K are as described above.
• B is O, C(O), O-C(O), C(O)-O, C(O)NH or C(O)N(R 8 ); more preferably B is O, C(O), O-C(O), C(O)-O, or C(O)N(R 8 ).
• the encapsulant may also contain a coupling agent.
• a coupling agent as used herein is a chemical species containing a polymerizable functional group for reaction with the maleimide and other vinyl compound, and a functional group capable of condensing with metal hydroxides present on the surface of the substrate.
• Such coupling agents and the preferred amounts for use in compositions for particular substrates are known in the art.
• Suitable coupling agents are silanes, silicate esters, metal acrylates or methacrylates, titanates, and compounds containing a chelating ligand, such as phosphine, mercaptan, and acetoacetate.
• coupling agents typically will be in amounts up to 10 percent by weight, and preferably in amounts of 0.1-3.0 percent by weight, of the maleimide and other monofunctional vinyl compound.
• the encapsulant compositions may contain compounds that lend additional flexibility and toughness to the resultant cured encapsulant.
• Such compounds may be any thermoset or thermoplastic material having a Tg of 50°C or less, and typically will be a polymeric material characterized by free rotation about the chemical bonds, such as can be obtained by the presence of carbon-carbon double bonds adjacent to carbon-carbon single bonds, the presence of ester and ether groups, and the absence of ring structures.
• Suitable such modifiers include polyacrylates, poly(butadiene), polyTHF (polymerized tetrahydrofuran), CTBN (carboxy-terminated butyronitrile) rubber, and polypropylene glycol.
• toughening compounds may be in an amount up to about 15 percent by weight of the maleimide and other monofunctional vinyl compound.
• siloxanes can be added to the underfill formulations to impart elastomeric properties.
• Suitable siloxanes are the methacryloxypropyl-terminated polydimethyl siloxanes, and the aminopropyl-terminated polydimethylsiloxanes, available from United Chemical Technologies.
• composition may also contain organic fillers, such as, polymers to adjust rheology.
• organic fillers such as, polymers to adjust rheology.
• Other additives known and used in the art may also be used for specific purposes, such as, adhesion promoters. The selection of the types and amounts suitable is within the expertise of one skilled in the art.
• compositions were investigated for viscosity and thixotropic index for the uncured composition, and for curing profile, glass transition temperature, coefficient of thermal expansion, thermal mechanical analysis, and reworkability for the cured composition.
• Dimer diamine (sold as Versamine 552 by Henkel, 20.0 g, 37 mmol) was solvated in diethyl ether (Et 2 O) (200 mL) in a 500 mL three-necked flask equipped with an addition funnel, magnetic stirring, internal temperature probe and nitrogen inlet/outlet.
• NaOH aq (11.7 mL of 6.25 M solution diluted with 100 mL H 2 O, 73 mmol) was added with vigorous stirring. This solution was placed under a steady flow of nitrogen and cooled to 3°C on an ice bath with stirring.
• the addition funnel was charged with p -nitrobenzoyl chloride (13.6 g, 73 mmol) in Et 2 O (50 mL), and this solution was added to the reaction vessel over the course of 60 minutes, maintaining an internal T ⁇ 10°C.
• the reaction was stirred at -3°C for an additional 60 minutes after this addition was complete, then allowed to warm to room temperature and stirred for another 4 hours.
• the solution was transferred to a separatory funnel and the isolated organic layer washed with distilled H 2 O (300 mL), 5% HCl aq (300 mL), NaCl aq (250 mL) and distilled H 2 O (2x250 mL).
• the dinitro compound described above (5.0 g, 5.9 mmol) was dissolved in methanol (MeOH) (25 mL) and tetrahydrofuran (THF) (5 mL) in a 250 mL three-necked flask equipped with magnetic stirring, reflux condensor and nitrogen inlet/outlet. The solution was placed under nitrogen, and 5% Pd-C (0.96 g) were added with stirring. Ammonium formate (3.4 g, 55 mmol) was added and the reaction stirred at room temperature for 2 hours. Carbon dioxide evolution was immediately observed. The reaction solution was filtered, and bulk filtrate solvent was removed via rotary evaporator.
• Emulsions were broken by adding NaCl when necessary.
• the organic layer was isolated, dried over MgSO 4 anhyd. and solvent removed in vacuo to yield the bismaleimide, a brown solid (2.0 g, 83%).
• the resin exhibited satisfactory 1 H NMR, 13 C NMR and IR spectra, which indicated slight contamination with acetic acid.
• the solution was removed from the freezer and allowed to warm to room temperature. Hydroquinone (0.0513 g) was added to the solution. A partial strip of the THF was carried out on a rotary evaporator with the temperature maintained below 28°C. The solution was concentrated to approximately 800 ml. Much particulate matter was visible. The solution was placed in freezer overnight.
• the mixture was removed from the freezer and allowed to warm.
• the solids were filtered, rinsing with THF.
• the filtrate was transferred to a 2 L multi-neck flask equipped with a mechanical stirrer, vacuum line connected to a trap, and a glass tube attached by tubing to a drying tube.
• the remaining THF was stripped at room temperature by pulling a vacuum and bubbling air through the material while stirring.
• the resultant thick, creamy-tan colored semi-solid was placed in the freezer overnight.
• the semi-solid was removed from the freezer and allowed to warm.
• the semi-solid was dissolved in 450 ml each of methanol and hexane, and washed with 50% methanol/water (4 x 250 ml) to remove 1-hydroxybenzotriazole (HOBT). It was attempted to extract the product with hexane. After addition of 300 ml of hexane separation was not observed. The mixture was washed with additional water (3 x 250 ml). The organic phase was placed in the freezer overnight.
• the material was removed from the freezer. Two layers were apparent. The upper layer was clear and yellow in color. The bottom layer was a orange and cloudy. The material was poured cold into a separatory funnel. The top layer was hexane and the desired product. The bottom layer was extracted with hexane (6 x 200 ml), separation occurred easily. The combined extracts were dried over anhydrous magnesium sulfate and filtered, rinsing the solids with hexane. The solvent was stripped to an approximate volume of 750 ml on a rotary evaporator with the temperature not exceeding 24°C. The remaining solvent was stripped off using a vacuum/air bubbling set-up at room temperature to give the desired product in 67% yield.
• Tris(epoxypropyl)isocyanurate (99.0 g, 0.33 mol) is dissolved in THF (500mL) in a 2 L three-necked flask equipped with mechanical stirrer, internal temperature probe and nitrogen inlet/outlet.
• hyroxyphenylmaleimide (189.2 g, 1 mol)
• benzyldimethylamine 1. g, 0.05 wt. %).
• the solution is heated to 80°C for 7 hours.
• the reaction is allowed to cool to room temperature, is filtered, and the filtrant washed with 5 % HCl aq (500mL) and distilled H 2 O (1 L).
• the resulting solid, triazinetris(maleimide) is vacuum dried at room temperature.
• Palmitoyl chloride (274.9 g, 1 mol) is dissolved in Et 2 O (500 mL) in a 2 L three-necked flask equipped with mechanical stirrer, internal temperature probe, addition funnel and nitrogen inlet/outlet.
• NaHCO 3 (84.0 g, 1 mol) in distilled H 2 O (500 mL) is added with vigorous stirring and the solution cooled on an ice bath under nitrogen.
• the addition funnel is charged with hydroxyethylmaleimide (141 g, 1 mol) in Et 2 O (100 mL) and this solution added to the reaction over a period of 30 minutes, maintaining an internal T ⁇ 10°C during the addition.
• the reaction is stirred for another 30 minutes on ice, then allowed to warm to room temperature and stirred for 4 hours.
• the reaction is transferred to a separatory funnel and the isolated organic layer washed with distilled H 2 O (500 mL), 5% HCl aq (500 mL) and distilled H 2 O (2x500 mL).
• the organics are isolated, dried over MgSO 4 anhyd., filtered and solvent removed in vacuo to yield the aliphatic maleimide.
• Bis(benzonitrile)palladium chloride (1,15 g, 5 mmol) is dissolved in a mixture of propyl vinyl ether (24.4 g, 3 mol) and oleic acid dimer diol (sold as Pripol 2033 by Unichema, 284.4 g, 500 mmol) in 2 L three-necked flask equipped with a mechanical stirrer under nitrogen. The solution is stirred for three days at room temperature, and then poured onto activated carbon (20 g) and stirred for 1 hour. The resulting slurry is filtered, and excess propyl vinyl ether removed in vacuo to yield the divinyl ether as a yellow oil.
• Oleic acid dimer diol (sold as Pripol 2033 by Unichema, 284.4 g, 500 mmol) is dissolved in dry acetone (500 mL) in a 1 L three-necked flask equipped with mechanical stirrer, addition funnel and internal temperature probe under nitrogen. Triethylamine (101.2 g, 1 mol) is added to this solution and the solution cooled to 4°C on an ice bath. Acryloyl chloride (90.5 g, 1 mol) solvated in dry acetone (100 mL) is charged into the addition funnel and added to the stirred reaction solution over the course of 60 minutes, maintaining an internal temperature ⁇ 10°C.
• Dimer acid (sold under the trademark Empol 1024 by Unichema) (574.6 g, 1 mol) and propargyl alcohol (112.1 g, 2 mol) were solvated in toluene (1 L) in a 3 L three-necked flask equipped with mechanical stirring and a Dean-Stark distillation apparatus. Concentrated H 2 SO 4 (6 mL) was added and the solution refluxed for 6 hours until 36 mL of H 2 O was azeotropically distilled. The solution was allowed to cool to room temperature, washed with H 2 O (2X1L), dried over MgSO 4 anhyd. and solvent removed in vacuo to yield the propargyl ester intermediate as an oil.
• This ester intermediate (650.7 g, 1 mol) was solvated in THF (200 mL) in a 1L three-necked flask equipped with reflux condensor, mechanical stirrer and internal temperature probe under nitrogen.
• Lauryl mercaptan 404.8 g, 2 mol
• 2,2'-azobis(2,4-dimethylpentanenitrile) (sold under the trademark Vazo 52 by DuPont) (11 g) were added and the resulting mixture heated to 70°C on an oil bath with stirring for 7 hours. The reaction was allowed to cool to room temperature and solvent removed in vacuo to yield the mercaptan as an oil.
• Underfill encapsulant compositions were prepared by mixing together the organic components and then by blending the components with a silica filler under high shear until homogeneous. The resulting compositions were light yellow slurries. The viscosities were measured by a Brookfield Viscometer using a 2.54cm spindle at 0.5 rpm at 25°C. The organic components, silica ratio by weight, Brookfield viscosity and thixotropic index are reported here:
• composition 11-A is a composition of Composition 11-A:
• the organic components were mixed with silica filler in a ratio of 40% by weight organic components to 60% by weight silica.
• the Brookfield viscosity was 21000 cp and the thixotropic index was 2.1.
• composition 11-B is a composition of Composition 11-B:
• the organic components were mixed with silica filler in a ratio of 33% by weight organic components to 67% by weight silica.
• the Brookfield viscosity was 15600 cp and the thixotropic index was 2.1.
• composition 11-C is a composition of Composition 11-C:
• N-dodecylphenylmaleimide 34.1g (0.1mol) isobornyl methacrylate 22.2g (0.1mol) aminopropyltrimethoxy silane t-butyl perethylhexanoate 00.56g (1 wt%)
• the organic components were mixed with silica filler in a ratio of 40% by weight organic components to 60% by weight silica.
• the Brookfield viscosity was 14300 cp and the thixotropic index was 2.5
• composition 11-D is a composition of Composition 11-D:
• the organic components were mixed with silica filler in a ratio of 39% by weight organic components to 61% by weight silica.
• the Brookfield viscosity was 21000 cp and the thixotropic index was 2.4.
• composition 11-E is a composition of Composition 11-E:
• N-dodecylphenylmaleimide 34.1g (0.1mol) t-butyl styrene 16.0g (0.1mol) aminopropyltrimethoxy silane t-butyl perethylhexanoate 00.5g (1 wt%)
• the organic components were mixed with silica filler in a ratio of 40% by weight organic components to 60% by weight silica.
• the Brookfield viscosity was 21000 cp and the thixotropic index was 2.3.
• the coefficient of thermal expansion is the change in dimension per unit change in temperature for a given material. Different materials will have different rates of expansion, and rates of expansion for any given material will vary with the temperature. If the CTE is very different for elements attached together, thermal cycling can cause the attached elements to bend, crack, or delaminate.
• the CTE of the chip is in the range of 2 or 3 ppm/°C; for organic circuit board substrate, the CTE is greater than 30 ppm/°C; and for the solder interconnect, the CTE is 26-28 ppm/°C.
• the CTE of the underfill encapsulant is best close to that of the solder.
• the glass transition region When a polymer is subjected to the application of heat, it will move through a transition region between a hard, glassy state to a soft, rubbery state. This region is known as the glass transition region or Tg. If a graph of expansion of the polymer versus temperature is plotted, the glass transition region is the intersection between the lower temperature/glassy region coefficient of thermal expansion and the higher temperature/rubbery region coefficient of thermal expansion. Above this region, the rate of expansion increases significantly. Consequently, it is preferred that the glass transition of the polymer be higher than normal operating temperatures experienced during the application, and if reworkability is needed, that the glass transition be lower than any rework temperature.
• the glass transition temperature (Tg) and the coefficient of thermal expansion (CTE) were measured using Thermal Mechanical Analysis on cured samples.
• a 2ml aliquot of each of the Compositions was injected into the 4mm cavity of a silica/rubber mold and cured to form a resinous cylinder of 4mm in diameter and 5mm in height. These samples were heated in a continuum of temperature ranging from -50°C to 200°C at a rate of increase in temperature of 5°C/minute.
• the Tg was measured as the temperature in °C at which the sample softened, determined as the breakpoint in the curve of expansion versus temperature.
• the CTE was measured as the slope of the expansion curve in units of ppm/°C.
• composition 11-A to 11-E was tested for reworkability using as a test vehicle a 250X250 mil 2 silicon die bonded to a FR-4 circuit board substrate.
• a one ml aliquot of underfill sample was blended with 0.002g of 3mil glass bead spacers (to take the place of solder or polymer interconnects), dispensed between the die and the FR-4 board, and cured at 125°C for 20 minutes.
• the assembly was heated on a 200°C hot plate for one minute.
• the die was mechanically removed, leaving underfill residue on the FR-4 board.
• the board was cooled to room temperature and methyl isobutyl ketone on a sponge swab was used to dissolve and clean the residue from the board.
• the recovery time for the rework was two minutes. All samples demonstrated reworkability.
• a 250X250 mil 2 silicon die was connected to a soldermask-coated substrate using a tin/lead solder.
• the underfill compositions 11-A to 11-E were individually dispensed along one side of individual dies and the substrate heated to 80°C to initiate the capillary action to fill the gap between the die and substrate.
• the assembly was then put into a 150°C oven for 10 minutes to cure the underfill.
• the assembly was heated on a 200°C hot plate for one minute, after which the die was mechanically removed from the board.
• the underfill material had softened and the solder interconnect had melted, leaving residues of both solder and underfill on the board.
• a sponge swab saturated with methyl ethyl ketone solvent was used to remove the underfill and clean the board until no residual material was observable under an optical microscope.
• An underfill encapsulant composition containing both mono-functional and polyfunctional compounds were prepared by mixing together the organic components and then by blending the components with a silica filler under high shear until homogeneous. The resulting compositions were light yellow slurries.
• N-4-butylphenyl maleimide 22.9g (64.9%) 4-hydroxybutyl vinyl ether 11.6g (32.9%) triethylene glycol divinyl ether 0.2g (0.57%) methacyloxypropyl trimethoxysilane 0.3g (0.85%) dicumyl peroxide 0.3g (0.85%).
• the organic components were mixed with silica filler in a ratio of 34% by weight organic components to 66% by weight silica (68.5 g) (sold by Denka, product number FB-6S).
• the CTE was measured as 34ppm/°C, Tg is 135°C.
• the sample was cured as in Example 13 and no residual material was observable under an optical microscope.
• An encapsulant composition was prepared by combining the following ingredients with vigorous manual mixing until a homogenous paste was obtained: Bismaleimide (prepared from polytetramethylene oxide-di- p -aminobenzoate, sold as Versalink P-650 by Henkel) 1.01 g Cyclohexanedimethanol divinylether (International Specialty Products): 0.19 g ⁇ , ⁇ -Dimethoxy- ⁇ -phenylacetophenone (sold as Irgacure 651 by Ciba Specialty Chemicals) 0.06 g Hydrophilic Fused Silica (sold by Denka, ⁇ 5 micron) 3.78 g
• a 250 mil x 250 mil silicon die placed on FR-4 laminate was encapsulated with the above paste and irradiated for 30 seconds using a pulsed xenon UV source (RC-500B Pulsed UV Curing System, Xenon Corporation).
• the encapsulant exhibited a hard, fully cured surface and held the die firmly to the laminate material when force was applied.
• the sample assembly was subsequently placed in a 175°C oven for 20 minutes.
• the encapsulated die was allowed to cool to room temperature and then forcibly removed from the laminate. No regions of uncured encapsulant were detected around the die edge, the laminate/adhesive interface or the adhesive/air surface interface.
• An encapsulant composition was prepared by combining the following ingredients with vigorous manual mixing until a homogenous paste was obtained: Bismaleimide (prepared from polytetramethylene oxide-di- p -aminobenzoate, sold as Versalink P-650 by Henkel) 1.01 g Cyclohexanedimethanol divinylether (International Specialty Products): 0.19 g t -Butyl-2-ethylhexanoate 0.03 g Hydrophilic Fused Silica (sold by Denka, ⁇ 5 micron) 3.78 g A 250 mil x 250 mil silicon die placed on FR-4 laminate was encapsulated with the above paste and placed in a 150°C oven for 30 min. The test assembly was allowed to cool to room temperature and the die was forcibly removed from the laminate. No regions of uncured encapsulant were detected around the die edge, the laminate/adhesive interface or the adhesive/air surface interface.
• inventive method include, but are not limited to, those designated in the following numbered paragraphs:

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